It is proposed to extend our studies in defining transporting properties of the rat testicular and epididymal epithelium. The transport of amino acids (3H-Alpha-amino-isobutyric acid and 14C-cycloleucine) and a dipeptide, 14C-carnosine (Beta-alanyl-L-histidine) into the rat testicular and epididymal tissue and lumen, and their transport out of the lumen will be studied. By the use of in vitro incubations of testicular and epididymal tissue (caput, corpus and cauda) under varying conditions, it is planned to define the existence of specific amino acid and dipeptide transporting sites on their basolateral membranes. Similarly, by using in vivo microperfusion techniques, the lumen of the seminiferous tubule and epididymal duct (caput, corpus and cauda) will be perfused with the above amino acids and the dipeptide under varying conditions. Thus, specific transporting sites for these substances can be defined for the luminal membrane. Further experiments will be performed to determine whether there are exchange or counter-transport systems for amino acids operating across the epithelium of the seminiferous tubule and epididymal duct. The morphology of the testicular and epididymal epithelial cells after each experimental manipulation will be examined using light microscopy, and in selected instances their ultrastructure will be studied. The secretion and absorption of different organic solutes into and out of the seminiferous tubule and epididymal duct produce a milieu or microenvironment which appears to be important for sperm development, maturation and survival. A further understanding of the complex interaction between the epedidymal epithelium, microenvironment and the spermatozoa will provide information fundamental to the development of a male contraceptive and treatment of some forms of male infertility.